Variable resistance device



Oct. 11, 1938.

M. J. ARYIN 2,132,594

VARIABLE RES I STANCE DEVICE Filed Oct. 31, 1936 III/{IIIIIIIIIII "walla/11 011,111 1 INVENTOR UAR/0N J ARV/N ATTORNEY Patented Oct. 11, 1938 PATENT OFFICE VARIABLE RESISTANCE DEVICE Marion J. Arvin, Indianapolis,

Ind., assisnor to P. R. Mallory & 00.. Inc., Indianapolis, Ind., a corporation of Delaware Application October 31, 1936, Serial No. 108,588

Claims. This invention relates to resistance devices and more particularly to variable devices comprising an arcuate resistance element and a moving contact therefor.

An object of the present invention is to improve the construction of such devices.

Other objects of the invention will be apparent from the following description and accompanying drawing taken in connection with the appended claims.

The invention comprises the features of construction, combination of elements, arrangement of parts, and methods of manufacture and operation referred to above or which will be brought out and exemplified in the disclosure hereinafter set forth, including the illustrations in the draw.- ing.

In the drawing:

Figure 1 is a face view of a variable resistance device embodying one form of the present in- .vention;

Figure 2 is a section on the line 2-2 of Figure 1, and

Figure 3 is a perspective view of for said device.

While a preferred embodiment of the invention is described herein, it is contemplated that considerable variation may be made in the method of procedure and the construction of parts without departing from the spirit of the invention. In the following description and in the claims, parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

In variable resistance devices, rheostats or potentiometers, particularly those comprising a winding of resistance wire, such as are used for volume controls in radio sets, the resistance element is commonly enclosed within a cylindrical casing. It is a common practice, for example, to wind the resistance wire on a strip of insulatlng material, such as uncured Bakelite fibre, which is then bent into a circular shape to conform to the inside wall of a cup or housing. Since the housing is usually formed of metal, it is necessary to provide a lining of insulating material between the wall of the housing and the circular resistance element. It is also necessary to secure the element within the housing in some positive manner so that it will not become loose during operation or after long periods of time. Various methods have been used in the past for securing the resistance element within the housing, such as riveting and clamping. These methods are a spring wedge relatively costly and it is necessary to shape the terminals so that they will clamp positively on the ends of the resistance element. The use of a solid wedge between the ends of the strip of insulating material is unsatisfactory because of loosening as a result of heating or drying out of the insulating strip, with a resultant tendency toward shrinkage.

In accordance with the present invention a positive permanent anchoring means is provided for the resistance element comprising a spring member interposed between the ends of the element so as to hold the parts together under compression at all times.

Referring to the drawing, Figure 1 shows a face view of a variable resistance device in, with the cover removed and Figure 2 shows a section through this device showing the details of the improved spring wedge arrangement of the present invention. The device ill comprises a metal shell or cup I I having a cylindrical side wall [2 and a flat end wall I3. Disposed within.she1l l l and resting against the walls thereof are lining members of sheet insulating material, such as sheet Bakelite, one of said members comprising a disc I disposed against end wall l3 and the other of said members comprising a cylindrical strip l5 disposed against the cylindrical wall l2 of the cup.

The resistance element It, comprising a re- 3 sistance wire I! wound on a Bakelite strip I8, is bent into generally cylindrical shape so as to fit within cup with its outer surface against lining member [5 and one of its edges against lining member I. A pair of terminal lugs I9 and 20 pass through openings 2| and 22 in wall l2 of the cup and through openings in lining member I5, the inner ends of lugs l9 and 20 making electrical connection with the respective ends of the resistance winding IT. A third terminal lug 23 passes through the wall of the cup and between the ends 24 and 25 of strip I 8 and connects to rotatable contact member 26 in the center of the cup. Member 26 carries a sliding contact portion 21 which slides along the free edge of resistance winding l! for varying the resistance of the device.

In order to hold the resistance element securely in place atall times, spring wedge 28 (see Fig. 3) is inserted between the ends 24 and 25 of strip I8. 50 Spring wedge 28 comprises a U-shaped piece of spring metal, such as bronze or the like. The wedge 28 is preferably formed with small projections 29 and 30 on the outside edges of the arms of the U, at the ends thereof, which projections become embedded in the ends of strip l8 when the spring wedge is forced into position. Projections 29 and 30 may merely comprise the burr, incident to shearing the metal used to form the U-shaped spring element.

Since strip I8 is commonly formed of Bakelite or some other synthetic resin material or resinimpregnated fibres, it may have a tendency to shrink upon heating or drying out. The spring wedge 28 is inserted between the ends of the element under compression so that it applies a constant expanding force to the element l8, thereby tending to hold the entire element securely against the wall of the well. Should the element shrink at any time during its life, the spring wedge will expand and remain pressed firmly against the ends so as to maintain the element securely wedged within the case at all times.

With this arrangement, it may, in some instances, be unnecessary to form a special connection between terminals i9 and 20 and the wire of the resistance element since the pressure of the spring wedge will normally be sufficient to hold the ends of the resistance winding firmly against the terminal members.

While the present invention, as to its objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

I claim:

1. A variable resistance device comprising a cylindrical casing and a resistance element therein, said element comprising a strip of material bent to conform to the cylindrical wall of said casing with the ends thereof spaced apart along the wall of said casing and a U-shaped spring wedge between said ends with the arms thereof disposed in engagement with said ends and held in compression by said ends.

2. The combination with an enclosing cup having'a circular wall; of a generally circular resistance unit surrounded by the circular wall of.

the cup and having adjacent end portions; and a spreading device engaging said end portions and exerting expanding action upon the resistance unit in a circular direction to press the resistance unit against the circular cup wall to hold the resistance unit in assembly with the cup, said spreading device comprising a U-shaped spring wedge inserted between said end portions with the arms thereof in engagement with the end portions and held under compression solely by engagement with said end portions.

3. A variable resistance device comprising an enclosing cup having a cylindrical wall, a resistance unit surrounded by the cylindrical wall of the cup and comprising a strip of sheet insulating material and a winding of resistance wire thereon, said unit being bent into generally cylindrical shape with the ends thereof adjacent each other, and a spreading device engaging said ends and exerting expanding action upon the resistance unit in a circular direction to press the resistance unit against the circular cup wall to hold the resistance unit in assembly with the cup, said spreading device comprising a U-shaped spring wedge with the arms of said wedge disposed along said ends, said wedge being held under compression by engagement with said end portions.

4. A variable resistance device comprising an enclosing cup having a cylindrical wall, a resistance unit surrounded by the cylindrical wall of the cup and comprising a strip of sheet insulating material and a winding of resistance wire thereon, said unit being bent into generally cylindrical shape with the ends thereof adjacent each other, and a spreading device engaging said ends and exerting expanding action upon the resistance unit in a circular direction to press the resistance unit against the circular cup wall to hold the resistance unit inassembly with the cup, said spreading device comprising a U-shaped spring wedge with the arms of said wedge disposed along said ends, said arms having projections embedded in said ends, and said wedge being held under compression by engagement with said end portions.

5. The combination with an enclosing cup having a circular wall, of a generally circular resistance unit surrounded by the circular wall of the cup and having adjacent end portions, said resistance unit having a tendency to shrink with age or change of condition, and a spreading device engaging said end portions and exerting expanding action upon the resistance unit in a circular direction to press the resistance unit against the circular cup wall to hold the resistance unit in assembly with the cup, said spreading device comprising a U-shaped spring wedge inserted between said end portions with the arms thereof in engagement with the end portions and heldunder compression solely by E subsequent adjustment.

MARION J. ARVIN. 

